Recent advances in wireless communication technologies have enabled rapid evolution of communication system technologies. Among these, the LTE system has attracted much attention as a fourth generation mobile communication technology. The LTE system not only supports basic handover between cells having been supported by previous generation communication technologies but also supports handover in a variety of scenarios.
For example, the LTE system supports recovery from failure in a handover attempt. The LTE system also supports handover between heterogeneous cells. Here, heterogeneous cells may include a macro cell covering a wide area, a picocell covering a small area, and a closed subscriber group (CSG) cell to which only a specific group of subscribers are allowed to connect.
First, consider a case where a user equipment fails in handover. Several options are available when the user equipment performs handover from a source cell to a target cell. For example, after handover not involving full configuration option, the user equipment in the target cell may use settings most inherited from those settings configured in the source cell. After handover involving full configuration option, the user equipment in the target cell may have to newly configure all settings. The full configuration option applies when it is difficult for the target cell to inherit settings from the source cell. The user equipment may determine whether to reset existing parameters according to the above two options.
Meanwhile, when a handover command with the full configuration option is received from the source cell, the user equipment may reset existing parameters. Thereafter, owing to handover failure, the user equipment may have to return to the source cell and perform connection reestablishment and reconfiguration by reuse of the existing parameters. However, as the existing parameters have been reset, they may be not reusable. This is a problem to be addressed.
Second, consider a case where a user equipment performs handover from a source macro cell to a target CSG cell. As a special group of subscribers are allowed to access a CSG cell, to hand over a user equipment to the CSG cell, the network should be able to determine whether the user equipment is a member of the CSG cell. To this end, in the exiting procedure, when a user equipment reports signal measurement results to the source cell, the user equipment reports the CSG ID of a measured cell and a CSG member indication indicating whether the user equipment is a member of the measured CSG cell.
The above procedure is applicable when the target CSG cell is operated by a single operator. However, in the case wherein the target CSG cell is operated by multiple operators, the scheme to report the operator to which the target CSG cell belongs is not specified. This is another problem to be addressed.